With the development of modern molecular biology, it is now possible to isolate individual genes from organisms virtually at will. This has placed within the realm of possibility the genetic manipulation of economically important agricultural plants. Desirable goals include the development of plant varieties with new traits such as improved nutritional quality, productivity, disease resistance, and drought and salinity tolerance. The major obstacle to the realization of these goals is lack of an agent or "vector" for the stable introduction of foreign genes into plant cells.
Bacteria of the genus Agrobacterium have the capacity to induce crown gall tumors in dicotyledonous plants. The genetic determinant responsible for this tumorous transformation is carried by large plasmids, called Ti plasmids, present within these bacteria. This is a natural system for the transformation of plant cells, and it has been shown to be due to the stable integration of at least a part of the Ti plasmid (the so-called T region) into the host plant cell genome. The T region DNA sequences which occur covalently attached to plant DNA in transformed cells are the same in different tumor lines. This means that the DNA sequences responsible for integration of the T region are precisely defined.
It would be desirable to provide a plant vector having the functional portions of the T region DNA sequences but incapacitated in respect of its ability to induce plant tumor formation, and this is the subject of the present invention.